Unfortunately, opening up your Apple Watch may damage the NFC antenna, which also serves as a gasketing seal. The antenna is made up of two layers, glued together. These layers may separate when you open your watch, compromising its seal after reassembly. If this happens, you'll need to repair or replace your antenna before reassembling your watch.
Be sure to follow our [guide|41083] guide when you're done.
Replace or repair the NFC antenna/front gasket on your Apple Watch.